1. Field of the Invention
This invention relates to a method and apparatus for minimizing the electrostatic charges developed in transient flowing fluids, such as hydrocarbon fuels, using the corona discharge method.
The accumulation of electrical charges in a moving fluid has long been a problem to the safe handling of flammable liquids. There are numerous instances where static charges have accumulated to levels high enough to cause a discharge of sufficient intensity that ignition of the flammable liquid resulted.
The most prevalent of the electrostatic-induced accidents has been in connection with tank truck and storage vessel loading operations. The spark discharge in such instances occurs between the surface of the charged fluid in the tank or vessel and some component of the tank or vessel system such as reinforcing members, gauge markers, or the loading spout. This type of sparking is internal and can occur whether or not the tank or vessel is grounded to the loading pipe assembly.
A number of methods have been employed to reduce the safety hazards involved in handling flammable hydrocarbon fluids. Among them are: (a) relaxation tanks wherein the charge on the liquid is allowed to dissipate naturally, in the absence of air, before the liquid enters the receiving tanks (b) the use of a static dissipater additive to increase the conductivity of the liquid and thereby promote the rapid dissipation of charge, and (c) the static charge neutralizer, which employs pointed electrodes protruding from a plastic lining of a pipe into the flowing liquid to dissipate the charge by means of a lightning rod effect. Relaxation tanks are impractical where low-conductivity liquids must be moved at high flow rates since the size of the tank required to reduce the charge on the liquid to a safe level becomes prohibitively large. Although the static dissipater additive protects the product during all phases of handling, it does have the disadvantage of interfering with the water separator characteristics in the instances where it's being used on a fuel. The static charge neutralizer employs a continuous corona inside the moving liquid to neutralize the charge.
As the quality of hydrocarbon products has improved, there has been increased demand for product cleanliness. As a result, filtering arrangements are being used in many liquid-hydrocarbon-handling systems. However, the filter is possibly the greatest single cause of static electricity buildup in such liquid-handling systems. This is mainly due to its large surface area which allows great amounts of charge separation at the filter surface and liquid interface. This mechanism results in the generation of high electrostatic charges. Also, there is a tendency to locate filters close to the loading point. The consequence of this is that when the liquid is discharged into a tank or vessel it is in a highly charged and dangerous condition.
2. Description of the Prior Art
U.S. Pat. No. 3,619,718 to Leonard discloses charge reduction methods utilizing the triboelectric effect of differing materials. Materials such as material made of glass tend to develop a positive electrostatic charge, while materials containing polyester resins tend to develop negative electrostatic charge. The electrostatic charge can be neutralized inside the cartridge by using materials which tend to develop opposite charges of opposite polarity. However, filter media vary in fiber diameter, density, surface coatings, etc. which makes this approach very difficult in practice. In addition, industry qualification specifications require these filters to perform a variety of functions, which limit the opportunity to utilize the triboelectric effect in filter design.
Attempts have been made to neutralize the electrostatic charge by utilizing filters which impart opposite charges to the transient fluid as disclosed in U.S. Pat. No. 3,619,718, and were found to be unsuccessful.
It is an object of the present invention to produce an apparatus which will minimize the safety hazard caused by static electricity building in moving liquids.
Another object of the invention is to produce an apparatus which will prevent the buildup of electrostatic charges to levels high enough to cause an ignition spark in liquid hydrocarbon handling systems.
Still, a further object of the invention is to produce an apparatus to effect a neutralization of accumulated electrostatic charge upon a flowing hydrocarbon liquid.